The US is carrying out airstrikes in three countries across the Middle East. It has sent billions of dollars in military hardware and is providing tactical support for its closest ally in the region, which is embroiled in a war against one militant group and almost daily skirmishes with another on its northern border. US forces in two of those countries have been attacked more than 150 times in the last three months, and the de-facto ruling power in an impoverished country in the Red Sea has brought international shipping there to a grinding halt.